Early warning smoke detection

February 2018 Fire & Safety

The requirement for early warning smoke detection systems is increasing as applications becoming more diverse and the need to eliminate false alarms in order to ensure business continuity becomes more important.

Aspirating Smoke Detection (ASD), which uses a network of conduit piping connected to a high sensitivity detector, is the only technology available that is able to address these requirements. Using very specific design criteria, sampling holes are drilled into the conduit. An aspirator mounted inside the detector then actively draws the air through the pipe network and into a laser smoke detection chamber which analyses the level of smoke.

Early warning smoke detection is most commonly used in applications where business continuity is paramount, smoke is difficult to detect, maintenance of the smoke detection system is difficult, evacuation of the building is challenging, environmental conditions are difficult or where fire suppression systems are present. Through correct design and programming of the system, all these challenges can be met to ensure an efficient and effective smoke detection system.

A big advantage of using ASD systems in these areas is the multiple alarm levels that are available from the detector. ASD systems provide early warning which allow for investigation prior to going into full fire alarm. This early warning can prevent full evacuation of premises and can detect a higher ambient smoke level before catastrophic failure of equipment.

In fire detection systems, sensitivity is measured using percentage obscuration per metre (%obs/m). This essentially is the measurement of the amount of smoke that obscures your vision over a metre. A standard optical type point detector’s sensitivity ranges from 2.0%obs/m up to 5%obs/m, depending on a number of variables. With an ASD system, sensitivities can go as low as 0.001% which allows the fire to be detected during inception.

Standards for detection

ASD designs are governed by the EN54 part 20 standard. This standard stipulates the transport time, namely the time it takes smoke to reach the detection chamber from the farthest sampling point on the conduit network, as well as the sensitivity of each sampling point throughout the conduit network. EN54 part 20 is divided into three class levels, Class A, B and C.

Class A is the most sensitive and is the class required for very early warning smoke detection. Class A applications for ASD are commonly data centres, server rooms, MCC rooms and sub-stations. Class B, although not as sensitive as Class A, will still provide an early warning smoke detection system. Typical applications for a Class B ASD system would be cold rooms, clean rooms, laboratories and lamp rooms.

Class C allows for sensitivities similar to those achieved by standard fire detection systems and is normally used for areas where maintenance can be a problem or in areas with challenging environmental conditions. Applications suitable for a Class C design are warehouses, cold rooms and atriums.

When deciding on which ASD unit to use for a specific application, it is important to determine which design class is required for the application. When looking at various ASD options, it is important to see the maximum number of sampling holes per detector for each class. In many cases larger or multiple units are required.

The new VESDA-E range

VESDA by Xtralis has been a household name in ASD, also commonly referred to as High Sensitivity Smoke Detection (HSSD) or Early Warning Smoke Detection, for many years. Numerous VESDA LaserPlus, VESDA LaserScanner and VESDA LaserFocus having been successfully installed in various applications throughout Africa – all with a variety of challenges and system requirements.

After years of success, VESDA has now launched the next generation of VESDA Aspirating Smoke Detection Systems. The VESDA-E range of ASD has introduced new technology and functionality.

The big change VESDA made when developing the VESDA-E Range is the Flair detection chamber, or the VESDA Smoke+ system. The change in chamber allows the VESDA-E range to be up to 15 times more sensitive than its predecessors and competitor products. With the change of technology and introduction of the Flair chamber, the VESDA-E has the capability of distinguishing between smoke, wire smoke, diesel smoke and dust, thus preventing false alarms as well as providing environmental information on dust and diesel, should this be a requirement. The Flair chamber also allows the detector to maintain a consistent performance over a longer period even long-term exposure to smoke and dust.

All VESDA aspiration systems, including the new VESDA-E series, deliver absolute detection meaning that at no point does the detector adjust its sensitivity levels due to dust, age or contamination of the laser chamber. With a unique laser cleaning system, the VESDA system maintains the same sensitivities from day one throughout the duration of the detector’s life.

The new VESDA-E range has upgraded aspirators allowing longer pipe runs per unit, this together with the new Flair chamber technology, allows coverage of bigger areas without compromising on the sensitivity or effectiveness of the system. The VESDA-E range also uses a CMOS chip and the laser-sensing device within the Flair chamber to analyse the characteristics of the smoke. This technology together with various algorithms allow the detector to determine the type of smoke, as well as differentiate dust from smoke. The analytics fall into three categories namely WireTrace, DustTrace and DieselTrace, allowing the system to determine the threat during early stages of the fire or eliminate false alarms.

The new range of VESDA-E units offers four variations. These are the VEP 1-pipe unit, the VEP 4-pipe unit, the VEU and the VEA. The VEP is the newest addition to the VESDA-E family and has been introduced to replace the VESDA LaserPlus after 20 years of service. The VEU is the larger brother of the VEP, allowing longer pipe runs and higher sensitivity allowing Class A designs for larger areas. The VEA uses a microbore network for in-cabinet monitoring, large atriums and other applications that would require individually addressed ­sampling points.

The VESDA-E range offer various methods of monitoring, whether it be using the internal relays, VSM4 VESDA software, or the new iVESDA application that uses the unit’s on-board Wi-Fi, to allow you to monitor the entire VESDAnet from your phone or tablet.

For more information contact Technoswitch, +27 (0)11 794 9144, info@technoswitch.co.za, www.technoswitch.co.za


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